This application claims priority from co-pending provisional application Serial No. 60/214,825 filed on Jun. 28, 2000.
The U.S. Government has a paid-up license in this invention and a right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of National Institute of Health Grant No. DK 47659.
Uric acid is a purine metabolite that in most animals is degraded by the hepatic enzyme uricase to allantoin. However, several mutations of the gene for this enzyme occurred during early primate development with the consequence that man and other primates have relatively higher levels of serum uric acid [Wu, X., Muzny, D. M., Lee, C. C., and Caskey, C. T., Two independent mutational events resulted in the loss of urate oxidase during hominoid evolution. J Mol. Evol. 34:78-84 (1992)]. The adaptive benefit of this deletion is not known nor has the modern day consequences of these mutations been fully understood. It has been hypothesized that the loss of uricase provided a protective benefit to prehistoric man who was known to have a very low sodium diet [Eaton, S. B., Konner, and M., Paleolithic nutrition: A consideration of its nature and current implications. N Engl J Med 312: 283-289 (1985)] but in modem times these mutations resulted in the development of hypertension and other cardiovascular diseases. In most subjects, the loss of uricase appears to be of no significance, but for the 10 to 15 percent of the general population with the highest uric acid levels (>6.0 mg/dl in women and >6.5mg/dl in men), there is an increased risk for the development of hypertension, atherosclerosis, and other cardiovascular diseases. Additionally 25 to 50% of hypertensive individuals have elevated serum uric acid, based upon the current standards 7 mg/dl [Cannon, P. J., Stason, W. B., Demartini, F. E., Sommers, S. C., and Laragh, J. H., Hyperuricemia in primary and renal hypertension. N Engl J Med 275:457-464 (1966]. This invention demonstrates for the first time mechanistic evidence that uric acid is directly related to the development of increased blood pressure.
An association between an elevated uric acid and an increased risk for cardiovascular disease was originally suggested by Haig in the late 1800s. Haig postulated that uric acid crystals might precipitate in the circulation and occlude the microvasculature [Haig, A., On uric acid and arterial tension. Br Med J 1:288-291 (1889)], thereby assuming that the damaging effects of uric acid were related to the formation of uric acid crystals and not to the soluble form of uric acid. Recent epidemiological studies have reported that an elevated uric acid confers an increased risk for the development of hypertension [Selby, J. V., Friedman, G. D., and Quesenberry, C. P., Precursors of essential hypertension: pulmonary function, heart rate, uric acid, serum cholesterol, and other serum chemistries. Am J Epidemiol 131:1017-27 (1990); Jossa, F., et al. Serum uric acid and hypertension: the Olivetti heart study. J Hum Hypertens 8:677-681 (1994); and Goldstein, H. S., and Manowitz, P., Relationship between serum uric acid and blood pressure in adolescents. Annals Hum Biol 20:423-431 (1993)], ischemic heart disease [Fang, J., and Alderman, M. H. Serum uric acid and cardiovascular mortality. The NHANES I Epidemiologic Follow-up Study, 1971-1992 JAMA 283:2404-2410 (2000); Bengtsson, C., Lapidus, L., Stendahl, C., and Waldenström, J., Hyperuricemia and risk of cardiovasular disease and overall death. Acta Med Scand 224:549-55 (1988); and Alderman, M. H., Cohen, H., Madhavan, S., Kivlighn, S. Serum uric acid and cardiovascular events in successfully treated hypertensive patients. Hypertension 34:144-150 (1999).], and stroke [Lehto, S., Niskanen, L., Rönnemaa, T., and Laakso, M., Serum uric acid is a strong predictor of stroke in patients with non-insulin dependent diabetes mellitus. Stroke 29:635-639 (1998)]. In the Worksite study an increase of 1 mg/dl of uric acid conferred the same cardiovascular risk as an increase of 10 mm Hg in systolic blood pressure or 20 mg/dl of cholesterol [Alderman, M. H., Cohen, H., Madhavan, S., and Kivlighn, S., Serum uric acid and cardiovascular events in successfully treated hypertensive patients. Hypertension 34:144-150 (1999).]. Several studies have also reported that the increased mortality associated with diuretic use can be attributed to the increase in uric acid induced by these agents [Franse, L. V., Pahor, M., and Barli, M. D., Serum uric acid, it's change with diuretic use and risk of cardiovascular events in the Systolic Hypertension in the Elderly Program (SHEP). American Society of Hypertension Annual Meeting, May 1999, New York.]. Others have shown that an increased uric acid confers increased risk for cardiovascular mortality, especially in women [Fang, J., and Alderman, M. H., Serum uric acid and cardiovascular mortality. The NHANES I Epidemiologic Follow-up Study, 1971-1992 JAMA 283:2404-2410 (2000); Bengtsson, C., Lapidus, L., Stendahl, C., and Waldenström, J., Hyperuricemia and risk of cardiovasular disease and overall death. Acta Med Scand 224:549-55 (1988); and Persky, V. W., et al. Uric acid: A risk factor for coronary heart disease? Circulation 59:969-979 (1979)]. Despite the clinical and epidemiological evidence, some authorities do not consider an elevated uric acid to be a true cardiovascular risk factor [Vaccarino, V., and Krumholz, H. M., Risk factors for cardiovascular disease: One down, many more to evaluate. Ann Int Med 131:62-63 (1999); and Wannamethee, S. G., Is serum uric acid a risk factor for coronary heart disease? J Hum Hypertens 13:153-156 (1999)]. This is because many patients with an elevated uric acid have other well-established risk factors for cardiovascular disease, such as hypertension, renal disease, obesity, dyslipidemia, and insulin resistance [Barlow, K. A., Hyperlipidemia in primary gout. Metabolism 17:289-299 (1968) and Grahame, R., and Stott, J. T., Clinical survey of 354 patients with gout. Ann Rheum Dis 29:461-468 (1970)]. Whereas some studies have found that an elevated uric acid level is an independent risk factor after controlling for the contribution of these other risk factors by multivariate analyses [Fang, J., and Alderman, M. H., Serum uric acid and cardiovascular mortality. The NHANES I Epidemiologic Follow-up Study, 1971-1992 JAMA 283:2404-2410 (2000); Bengtsson, C., Lapidus, L., Stendahl, C., and Waldenström, J. Hyperuricemia and risk of cardiovasular disease and overall death. Acta Med Scand 224:549-55 (1988); and Persky, V. W., et al. Uric acid: A risk factor for coronary heart disease? Circulation 59:969-979 (1979)], other studies including the recent Framingham analysis could not [Culleton, B. F., Larson, M. G., Kannel, W. B., and Levy, D., Serum uric acid and risk for cardiovascular disease and death: The Framingham Study. Ann Intern Med 131:7-13 (1999); Klein, R., et al. Serum uric acid: its relationship to coronary heart disease risk factors and cardiovascular disease. Evans County, Georgia. Arch Int Med 132:401-410 (1973); and Yano, K., Reed, D. M., and McGee, D. L., Ten year incidence of coronary heart disease in the Honolulu Heart Program: relationship to biologic and lifestyle characteristics. Am J Epidemiol 119:653-666 (1984).]. The lack of a mechanistic pathway by which uric acid can cause cardiovascular disease, coupled with the inconclusive clinical and epidemiological data, have left this issue unresolved. In considering this controversy, it is important to note that no animal model existed to study the effects of a mildly elevated uric acid.
Cyclosporine (CSA) was introduced in the 1980's as an immunosuppressant, and quickly become a first line treatment in organ transplantation as well as in other immunologically mediated diseases [Bennett, W. M., De Mattos, A., Meyer, M. M., Andoh, T. F., and Barry, J. M., Chronic cyclosporine nephropathy. The Achille's heel of immunossupressive therapy. Kidney Int 1996; 50:1089.]. Cyclosporine has numerous side effects, of which two of the most important are nephrotoxicity [Myers, B. D. and Newton, L., Cyclosporine induced chronic nephropathy: an obbliterative microvascular renal injury. J Am Soc Nephrol 1991; 2: S45, and Chapman, J. R., Harding, N. G. L., Griffiths, D., and Morris, P. J., Reversibility of cyclosporine nephrotoxicity after three months treatment. Lancet 1985; 1:128.] and hyperuricemia [Gores, P. F., Fryd, D. S., Sutherland D. E. R., Najarian, J. S., and Simmons, R. L., Hyperuricemia after renal transplantation. Am J Surg 1988;156: 397.]. As many as 50% of patients taking CSA develop hyperuricemia [Kahl, L. E., Thompson, M. E., and Griffith, B. P., Gout in the heart transplant recipient: Physiological puzzle and therapeutic challenge. Am J Med 1989; 87: 289, Najarian, J. S., Fryd, D. S., and Stransd, M., A single institution, randomized, prospective trial of cyclosporine versus azathioprine-antilymphocyte globulin for immunossupression in renal allograft recipients. Ann Surg 1985; 201:142 and Sutherland, D. E. R., Fryd, D. S., and Strand, M. H., Minnesota randomized prospective trial of cyclosporine versus azathioprine-antilymphocyte globulin for immunossupression in renal allograft recipients. Am J Kidney Dis 1985; 5:318.] and 9 to 10% develop gout [West, C., Carpenter, B. J., and Hakala, T. R., The incidence of gout in renal transplant recipients. Am J Kidney Dis 1987; 10: 369.]. The hyperuricemia from CSA is thought to result from both a decrease in GFR [Zurcher, R. M., Bock, H. A., and Thiel, G., Hyperuricemia in cyclosporine treated patients: A GFR related effect. Nephrol Dial Transplant 1996; 11:153.], as well as an increase in net tubular urate reabsorption [Laine, J., and Holmberg, C., Mechanisms of hyperuricemia in cyclosporine-treated renal transplanted children. Nephron 1996; 74: 318, and Marcen, R., Gallego, N., Orofino, L. et al., Impairment of tubular secretion of urate in renal transplant patients on cyclosporine. Nephron 1995; 70: 307.]. The most important complication of CSA is nephrotoxicity, which is characterized histologically by striped interstitial fibrosis, tubular atrophy and arteriolar hyalinosis [Bennett, W. M., De Mattos, A., Meyer, M. M., Andoh, T. F., and Barry, J. M., Chronic cyclosporine nephropathy. The Achille's heel of immunossupressive therapy. Kidney Int 1996; 50:1089, Myers, B., Cyclosporine nephrotoxicity. Kidney Int 1986; 30:964, and Bennett, W. M., Burdmann, E. A., Andoh, T. F., Houghton, D. C., Lindsley, J., and Elzinga, L. W., Nephrotoxicity of immunossupressive drugs. Nephrol Dial Transplant 1994; 9:141.]. The pathogenesis of CSA nephropathy is multifactorial but likely involves afferent arteriolar vasoconstriction with activation of the renin angiotensin pathway and inhibition of nitric oxide (NO) production [Bennett, W. M., Burdmann, E. A., Andoh, T. F., Houghton, D. C., Lindsley, J., and Elzinga, L. W.: Nephrotoxicity of immunossupressive drugs. Nephrol Dial Transplant 1994; 9:141, Burdmann, E. A., Andoh, T. F., Nast, C. C., et al., Prevention of experimental cyclosporine induced interstitial fibrosis by losartan and enalapril. Am J Physiol 1995; 269: F491, and Pichler, R., Franceschini, N., Young, B. A. et al., Pathogenesis of cyclosporine nephropathy. Roles of angiotensin II and osteopontin. J Am Soc Nephrol 1995; 6: 1186.].
The possibility that cyclosporine induced hyperuricemia may have a role in either mediating or exacerbating cyclosporine nephropathy has not previously been considered. However, it is known that hyperuricemia is also associated with reduced renal blood flow and increased renal vascular resistance [Hoyer, P. F., Lee, I. K., Oemar, B. S., Krohn, H. P., Offner, G., and Brodhel, J., Renal handling of uric acid under cyclosporine A treatment. Pediatr Nephrol 1988; 2:18, and Messerli, F. H., Frolich, E. D., Drelinski, G. R., Suarez, D. H., and Aristimuno, G. G., Serum uric acid in essential hypertension: an indicator of renal vascular involvement. Ann Int Med 1980; 93:817.] and those patients with long-standing gout may develop chronic tubulointerstitial disease [Beck, L. H., Requiem for gouty nephropathy. Kidney Int 30:280-287, 1986, Emmerson, B. T., and Row, P. G., An evaluation of the pathogenesis of the gout kidney. Kidney Int. 1975; 8:65, and Johnson, R. J., Kivlighn, S. D., Kim, Y. G., Suga, S., and Fogo, A. B., Reapprasial of the pathogenesis and consequences of hyperuricemia in hypertension, cardiovascular disease and renal disease. Am J Kidney Dis 1999; 33: 225.]. Controversy has existed, however, over whether hyperuricemia is the cause or consequence of renal vasoconstriction and tubulointerstitial lesions [Nickeleit, V., and Mihatsh, M. J., Uric acid nephropathy and end-stage renal disease. Review of a non-disease. Nephrol Dial Transplant 1997;12: 1832, and Yü, T., Berger, L., Dorph, D. J., and Smith, H., Renal function in gout: V- Fators influencing the renal hemodynamics. Am J Med 1979: 67:766.].
A recent report suggested that allopurinol, an inhibitor of uric acid production, could protect the kidney from CSA nephrotoxicity [Assis, S. M., Monteiro, J. L., and Seguro, A. C., L-arginine and allopurinol protect against cyclosporine nephrotoxicity. Transplantation 1997; 63(8): 1070.]. Thus the hypothesis that hyperuricemia might exacerbate cyclosporine nephropathy was tested. As rodents normally do not become hyperuricemic because they have the hepatic enzyme uricase, which degrades uric acid to allantoin [Becker, B. F., Towards the physiological function of uric acid. Free Rad Biol Med 1993; 14:615, and Waisman, J., Bluestone, R. and Klinemberg, J. R., A preliminary report of nephropathy in hyperuricemic rats. Lab Invest 1974; 30:716.], rats with cyclosporine nephropathy, in the presence and absence of the uricase inhibitor, oxonic acid were compared. This invention demostrates that hyperuricemia exacerbates CSA nephropathy through a crystal independent mechanism.
Hyperuricemia, defined as serum uric acid levels >7.0 mg/dl in man and >6.0 mg/dl in women, is a common metabolic abnormality that is observed in 4 to 6% of the population (Wyngaarden J. B. and Kelley W. N., Epidemiology of hyperuricemia and gout. In Gout and Hyperuricemia, Grune and Stratton, New York, 1976, pp 21-37.). The major risks classically attributed to hyperuricemia have been the risk of developing gout and/or uric acid renal stones. Patients with longstanding hyperuricemia and/or gout are also at risk for developing chronic renal disease (Talbot, J. H., and Terplan, K. L., The kidney in gout. Medicine 39:405-467, 1960, and Gonick, H. C., Rubini, M. D., Gleason, I. O., and Sommers, S. C., The renal lesion in gout. Ann Int Med 62:667-74, 1965.). Several large studies have documented that between 30 and 60% of patients with gout will develop renal insufficiency and up to 10% will develop end stage renal disease (Talbot, J. H., and Terplan, K. L., The kidney in gout. Medicine 39:405-467, 1960; Gonick, H. C., Rubini, M. D., Gleason, I. O., and Sommers, S. C., The renal lesion in gout. Ann Int Med 62:667-74, 1965; Yü, T., Berger, L., Dorph, D. J., and Smith, H., Renal function in gout: V- Factors influencing the renal hemodynamics. Am J Med 67:766-71, 1979; and Berger, L., and Yü, T., Renal Function in Gout: IV. An Analysis of 524 Gouty Subjects Including long-term follow-up studies. Am J Med 59:605-613, 1975). Renal structural changes are even more common than the functional abnormalities (Greenbaum, D., and Ross, J. H., Renal biopsy in gout., Brit Med J 1:1502-1504, 1961.), and in one study renal disease was observed in 287 of 290 patients with gout (Talbot, J. H., and Terplan, K. L., The kidney in gout. Medicine 39:405-467, 1960.). The renal disease, which has been termed ‘gouty nephropathy’, is characterized by chronic tubulointerstitial fibrosis, often with arteriolosclerosis and glomerular sclerosis (Talbot, J. H., and Terplan, K. L., The kidney in gout. Medicine 39:405-467, 1960). In addition, many biopsies show focal deposits of urate crystals, particularly in the outer medulla (Talbot, J. H., and Terplan, K. L., The kidney in gout. Medicine 39:405-467, 1960; Gonick, H. C., Rubini, M. D., Gleason, I. O., and Sommers, S. C., The renal lesion in gout. Ann Int Med 62:667-74, 1965; and Cannon, P. J., Stason, W. B., Dematini, F. E., Sommers, S. C., and Laragh, J. H., Hyperuricemia in Primary and Renal Hypertension. New Engl J Med 275:457-464, 1966.).
However, investigators have challenged if ‘gouty nephropathy’ truly exists (Beck, L. H., Requiem for gouty nephropathy. Kidney Int 30:280-287, 1986, and Nickeleit, V. and Mihatsh, M. J., Uric acid nephropathy and end-stage renal disease. Review of a non-disease. Nephrol Dial Transplant 12: 1832-38, 1997.). Some studies have suggested that the renal functional changes could be attributed to co-existing hypertension or the consequence of aging (Yü, T., Berger, L., Dorph, D. J., and Smith, H., Renal function in gout: V- Factors influencing the renal hemodynamics. Am J Med 67:766-71, 1979, and Yü, T. and Berger, L., Impaired Renal Function in Gout: Its Association with Hypertensive Vascular Disease and Intrinsic Renal Disease. Am J Med 72:95-100, 1982). Others have noted the apparent discrepancy between the focal nature of the urate deposits and the diffuse interstitial disease ((Beck, L. H., Requiem for gouty nephropathy. Kidney Int 30:280-287, 1986, and Nickeleit, V. and Mihatsh, M. J., Uric acid nephropathy and end-stage renal disease. Review of a non-disease. Nephrol Dial Transplant 12: 1832-38, 1997.). Furthermore, the effect of uric acid lowering agents on improving renal function in patients with gout has been variable, with both positive (Perez-Ruiz, F., Calabozo, M., Fernandez-Lopez, M. J., Herrero-Beites, A., Ruiz-Lucea, E., Garcia-Erasukin, G., Duruelo, J., and Alonso-Ruiz, A., Treatment of chronic gout in patients with renal fundction impairment. An open, randomized actively controlled study. J Clin Rheumatol 1999; 5:49-55, and Perez-Ruiz F, Alonso-Ruiz A, Calabozo M, Herrero-Beites A, Garcia-Erauskin G, and Ruiz-Lucca E., Efficacy of allopurinol and benzbromarone for the control of hyperuricemia. A pathogenic approach to the treatment of primary chronic gout. Ann Rheum Dis 1998;57:545-549.) and negative (Fessel, W. J., Renal Outcomes of Gout and Hyperuricemia. Am J Med 67:74-82, 1979, and Rosenfeld, J. B., Effect of long-term allopurinol administration on serial GFR in normotensive and hypertensive hyperuricemic subjects. Adv Exp Med Biol 41B:581-596, 1974) studies reported.
A novel pathway has been demonstrated where uric acid, a purine metabolite present in the blood, actually causes hypertension and renal disease. It is known that markedly elevated uric acid can crystallize in the tubules of the kidney and cause kidney failure. The invention disclosed herein is that mildly elevated uric acid levels can also cause renal disease and hypertension. Furthermore, it has been shown that this action is mediated in part by activation of the renin-angiotensin system in the kidney and by the inhibition of nitric oxide synthases (NOS) within the kidney.